The pros, cons and energy-savings of triple-pane windows

Triple-pane glass is a sealed, insulated glass unit consisting of three panes of glass sandwiched together. Replacement windows began featuring triple glazing during the early '80s, because consumers wanted better-insulated windows.

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Homeowners and window manufacturers alike reasoned correctly that if two panes of glass were an improvement over one, three should achieve a better U-value than two. Low-emissivity (low-e) glass was still in its infancy and was expensive; few glass fabricators had the the proper equipment to make a sealed unit using low-e. Fueled by consumer demands for better insulated windows, the popularity of triple-pane glass grew for a while.

Today, triple-pane glass is making a comeback. While its advantages are many, there are a few minor drawbacks. Here are the pros and cons to consider when shopping for triple-glazed windows.

2 advantages of triple-pane windows

The two major advantages of triple-glazing are reduction of condensation and lower heating and cooling costs.

Window condensation is all but eliminated with triple glazing. If you have ever boiled water on a cold day, you have probably experienced condensation forming on your windows from the added indoor humidity. Triple glazing makes it more difficult for condensation to form, because it is harder for radiant heat to penetrate three layers of glass.

Heating and cooling costs are often lower. The graph below compares four different types of windows: single-glazed glass, double-glazed glass, double glazed with low-e glass, and triple glazed without low-e glass. The annual heating energy consumed for each type of window is shown in millions of BTUs used in three different climates--Madison, Wis., St. Louis, Mo. and Phoenix, Ariz.

According to the graph, triple-pane windows and double-pane windows with low-e coating are the most energy-efficent windows.

This graph from The Home Energy website, shows the cost savings possible for a 2,000-square-foot, single-family home in Boston. If you are replacing single-pane, aluminum windows with triple-pane, low-e coated, insulated-frame windows, you could save as much as 39 percent on your annual heating costs.

4 minor disadvantages

With every upside comes a downside, so consider these disadvantages of triple-glazed windows against the value of energy savings:

The sash is heavy to lift and may require as many as four balances on each. These could be visible.

Triple-pane windows require thicker frames to accommodate the extra pane of glass, which can increase difficulty of installation.

The added weight may make a tilt-out feature difficult to operate, making cleaning less convenient.

Visible light is decreased, making the view to outside darker, especially if low-e glass is used.

Many window manufacturers, like Energy-Guard, already offer triple glazing in their product line, and many more are sure to add them as consumer demand grows. If you want well-insulated windows, triple pane is one bet to see as a clear win.

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.